1. Field of the Invention
The present invention relates to a method for producing filled and reclosable pressure vessels, in which a vessel body with a cylindrical jacket and bottom part is filled with a fluid, whereupon it is non-detachably closed with a lid element and subsequently optionally subjected to a heat treatment, with a lid surface, preferably made of metal, and a closure means made of plastic being provided for use as a lid element, the closure means being fastened to a first surface of the lid surface, and at least one seal arranged on the closure means being brought into contact with at least one sealing surface arranged on the first surface of the lid surface, and the lid element formed by the lid surface and the closure means being arranged upon closing the pressure vessel in such a way that the closure means faces the interior of the sealed pressure vessel.
2. The Prior Art
Pressure vessels of the kind mentioned above are produced as recloseable beverage cans for example. In an especially advantageous embodiment of such beverage cans, an orifice is permanently provided in the lid surface, which is made of aluminum like the remainder of the can. This orifice is sealed by a closure means which rests on the lid surface in the interior of the can. This closure means carries a flap or a slide which can be actuated from the outside and which allows exposing the orifice for discharging the can and tightly sealing the can again after the first opening. Such a pressure vessel is disclosed for example in AT 507.950 AT of the applicant.
After the filling and closing, beverage cans are usually subjected to heat treatment in order to ensure the necessary sterility in that the content of the can is pasteurized. In this process, the can is briefly subjected to a temperature of over 60° C., as a result of which the pressure in the interior rises to several bars. The can is obviously deformed in this process, with especially the lid surface bulging to the outside. This bulging reverts back at least in part after cooling.
Similar effects can also occur by inadvertent heat treatment such as if the can is left in a motor vehicle for example and is subjected there temporarily to high temperatures which lead to a comparable pressure increase.
The increase in pressure is especially critical in cans which contain carbonated beverages, but it also occurs to a lower extent in other products.
It has now been noticed that beverage cans partly cannot be tightly sealed after pasteurizing and first opening. A deformation of the closure means in particular occurring in the course of the heat treatment and reverting back after cooling only partly was identified as the potential reason.
It is the object of the present invention to provide a method for producing a pressure vessel of the kind described above and especially with respect to a beverage can in which the performance of the required heat treatment does not have any negative effects on the reclosing ability and therefore the tightness of the pressure vessel.